The present invention relates to a yarn brake for use in weaving machines.
A yarn brake--as known from EP-A-326784 by Loepfe--comprises, in addition to the two fixed yarn guide elements, a swiveling bridge supporting two further yarn guide elements, aligned with the straight yarn path in the starting position of four rod-shaped braking elements. A certain distance is set between the rotation axis of the braking elements and the straight yarn path. The bridge rotates about a further rotation axis, essentially parallel to and spaced from the straight yarn path. The bridge is resiliently biased against the braking elements, in its swiveling direction, by repelling magnets positioned into the frame. As the brake is operated, the braking elements are caused to perform an angular movement about their rotation axis from the starting position, laterally across the straight yarn path, into the braking position on the other side of said path. Due to the tension produced in the yarn, deviated by the braking elements and by the fixed yarn guide elements, the bridge yields with a certain stroke against the force of the repelling magnets. The adjustment device allows to vary the position of the repelling magnets inside the frame, so as to vary the counter-force of the bridge and to thereby vary the degree of yarn deviation and the braking force acting on the moving yarn.
Another yarn brake--as known from EP-A-527510 by Picanol--provides for the rotation axis of the two rod-shaped braking elements to be positioned perpendicularly to the straight yarn path and to intersect said path. Both braking elements are positioned on a rotatable disk controlled by a rotation drive. The angular stroke of the braking elements about the rotation axis is limited by taps supported by the frame. The angular position of the taps is adjustable about the rotation axis of the braking elements through a set of screws engaging into a ring supporting the taps inside the frame. Adjusting the angular position of the taps requires a change in the angular stroke of the rotatable disk and of the rotation drive.
A similar yarn brake--known from U.S. Pat. No. 3,406,832 by Rempei--is provided with two spaced apart stop devices of the frame, which interfere with the oscillating path of a lever projecting sideways from the rotatable body carrying the braking elements. Two cables, fixed to opposite sides of the lever, are connected with drawing magnets operating the rotatable body in both rotating directions. The stop devices of the frame are thus apt to reduce the maximum angular stroke of the rotatable body. It is possible to vary the degree of yarn deviation in the braking position of the braking elements by adjusting the stroke of the drawing magnets.